6 J. PARSONS SCHAEFFER 



nasolacrimal passages. I, therefore, felt that there was need of 

 an investigation of the genesis of these passages in man, based 

 upon an examination of a larger number of human embryos than 

 was formerly done. Fortunately there were available for this 

 study good series of appropriately aged embryos showing the 

 genesis and early stages of the nasolacrimal passages. The 

 embryos ranged in age from thirty days to 'term.' A certain 

 amount of material of the early extra-uterine period was also 

 studied; together with a large number of adult specimens. 



It is well known that at one stage of the embryo there is a 

 furrow or fissure — the naso-optic fissure — extending from the eye 

 to the nasal pit. This fissure is bounded superiorly by the lateral 

 nasal process and inferiorly by the maxillary process. The naso- 

 optic fissure gradually disappears by a growth and coalescence 

 of the structures bordering it. In this manner the fissure is 

 'out-folded' as it were and thus becomes shallower and shallower 

 until its ultimate obliteration. The epidermis along the course 

 of the floor of the now very rudimentary fissure concerns us for 

 some time longer with reference to the anlage of the nasolacrimal 

 passages. 



Before the naso-optic fissure is entirely obliterated we have in 

 frontal sections a thickening of the deeper layers of the epidermis 

 along the floor of the very rudimentary fissure (fig. 2). This 

 initial thickening is the anlage of the nasolacrimal passages. It 

 is at first, and remains so for some time, a solid cord-like struc- 

 ture of epidermal cells, at all points a part of the epidermis, along 

 the floor of the remains of the naso-optic furrow, extending from 

 the neighborhood of the eye towards the nose. 



My observations began on embryos aged approximately from 

 thirty to thirty-two days. In these embryos I could find no 

 evidence whatever of an anlage of the nasolacrimal passages. 

 In fig. 1 we have a frontal section through the remains of the 

 naso-optic fissure (human embryo aged approximately thirty- 

 three days). Note that there is no evidence of the anlage of the 

 nasolacrimal passages along the floor of the rudimenatry fissure. 

 The epidermis appears uniform in thickness at all points, i.e., 

 the epidermis is not thickened along the floor of the fissure. 



